Automatic tuning control circuit



Aug. F ER AUTOMATIC TUNING CONTROL .CliRCUIT Filed Jan. .12, 1944 awa t-1% afl'ayo 1229.05 ,yJam ATTORNEY *3: INVENTOR l mescfiarzczfer Patented Aug. 14, 1945;

OFFICE AUTOMATIC TUNlNG ooNT ton'oIRoUrr l James F. Chandler, BuffalolNQYt, assignor to I Colonial Radio Corporation,Bufl*'alo, N. Y.

ApplicationJanuary 12, 1 944,i Serial No. 517,959

8, Claims. ,(Cl. 251F465 This invention relates to an automatic tuning control circuit, and more particularly to automatic crystal controlled radio transmiters or receivers, although it will be understood that my invention maybe applied in other apparatus where automatic tuning of a circuit to any one of a series of predetermined frequencies is desired. Various forms of circuits of this type have been described and claimed in a co-pending application of William S. Winfield, Serial No; 463,-

775; In apparatus of this type, the circuits are automatically tuned bya motor to desired frequencies determined by crystals, but do not require the setting of mechanical elements, such as pins, contactors, selecting cams, rocker bars, or the like. The Voltage developed in the circuit to be tuned is utilized to control a relay which opens the motor circuit. Since this voltage is zero except over the resonance range of the cir- H cult and is a maximum only at the resonant frequency or veryclose thereto, very accurate tuning can be obtained'in this. way. i

In experimental work with apparatus such as that describedin the above applicatiom'it has been found that, whilethe system described operates as contemplated when the resonance curves of the circuits controlled are separated or do not overlap to' any'considerable extent, difiiculties may be encountered when the channels desired to be tuned are so close to each other that the resonance curves overlap to a considerable extent Under such conditions the apparatus, whentune'd to one frequency, may remain tuned to that frequencyalthough the controls are operated to change the frequency.

It is an object of this invention to provide apparatus of the class described in which these difiiculties are eliminated and. reliability of operated to change the frequency channelj the crystal corresponding to the former channel is 1mmedi'ately disconnecte'd 'from the circuit, but the secondcrystalcorresponding to the new channel desired is not immediately connected into the circuit, thereby assuring" that the -motor which" drives the tuning instrumentality will be set into operation without the possibility of failurej. i i it l Still otherobjects and "advantages of my invention will be apparent from the specification.

"In the drawing,

l is'a circuit diagram of automatic tuning apparatus in' accordance with my invention. 16

Fig.2is a familyof'resonance curves illustrating conditions which may be encountered when it is desired to provide" a number of- "channels closely spaced in frequency.

Referring now more particularly to Fig. 1, reference numeral? designates a variable tuning instrumentality such as a variable condenser, variometer, or the like, driven by a suitable operating means,'such as motor 6, through suitable reduction gearing 6a, and serving to tune one or more circuits, which may i be oscillator icircuits, antennacircuits, or, in fact," any tunable circuit required tou be tuned, herein diagrammaticall The tuning instrumentality, which, forisjake of simplicity'fls referred. to as a condenser; although itfnmay, be'anothertinstrumentality, ,may be a s'ingle orlgangi condenser, and may tune'one or Cmore circuits, i as maybe desired; if.:.two or {more circuits arezdesired tobe simultaneously tuned.

The tuning instrumentalityais arranged for continuous rotation; i. e., no stop:iszprovidedrlimitingits rotation to 180 as is, sometimes the case yincondensersi For purposesof simplicity, thereation is assured, even though a number of channels are provided so closely adjacent in frequency that the resonance curves of the apparatus for various channels overlap. i

It is a further object of my invention to-provide apparatus which will be closely tuned to the desired channel even though other channels are closely adjacent to the desired channel.

It is a still further object of my invention to provideimproved apparatus of the class described having improved operational characteristics-such that the apparatus will function and tune properly even where channels are as closely spaced as tuningselectivity permits. w i

It is still a further object of my: invention to provide apparatus of the class,described soar,- ranged that when the selecting switch is oper- *mainden of the'tuning circuitzoncircuits is not shown, but it will be understoodthat: condenser 1 may be part of .work 'circuitl; voltage :derived from this circuit may be first rectified by rectifier 2, and then impressed, between the cathode 3a and controlielectrode'iib of relay control tube.q3. v t K.

W, The control tube ccntrolsthe operationof mctor 6 through "relays 4 and 5 connected in tandem. t The biasing and. plate voltages of. 1 control tube; 3=and its operating characteristics are so chosen and related to each other thatwhen the voltagederived, from work circuit l reaches a predetermined magnitudathe grid bias lonu t ube ,3 istsuch as to considerably reduce or stop the flow of plate current in tube 3., This permits the armature 4a (which maybe spring biasedto open position) to move away from fixed contact 4b, thereby opening the energizing circuit of motor relay 5 and likewise opening the circuit of clutch coil l4 operating mechanism (not shown) to immediately declutch the motor 6 from condenser and prevent the condenser from coasting past the resonance position due to the inertia opens, in turn opening relay '5, and thereby the of the motor and gearing. Opening of the circuit of the motor relay coil 5 permits the armature 5a, which maybespring biased to open position, to move away from fixed contact 5b, thereby deenergizing the motor. v

It may be noted at this point that the use of re-' lays 4 and 5 in tandem is of no significance with respect to my invention, but is desirable in case the motor current is so large that it cannot be properly handled by a relay operated by the plate current of tube 3. If this motor current is small enough, the relay winding 5 might be substituted for relay winding 4 without changing the principle of operation.

Selection of the various channels or frequencies to which the apparatus may be tuned is made by selecting switch [3, herein shown as movable from fixed contact I 311 to fixed contact I321.

It will be understood, however, that while two channelaany desired number of channels may be provided, each with its individual fixed contact and associated apparatus, as will now be described.

In the position 13a, a circuit is prepared from ground through switch [3, fixed contact l3a, and the energizing coil of relay I0, through armature Illa, fixed contact me, to the fixed contact 81), of'

cam switch 8; The circuit is open at the cam switch except at one position, through which it passes once in each tuning cycle. The cam is synchronized withtuning condenser 1 so'that closure of movable contact 8a against fixedcontact 8b duced? in the work circuit, no voltage is impressed on controltube3, normal plate current flows, re-

lays 4' and 5 are closed, and themotor circuit is energized. The motor will continue to operate until a voltage is produced in the work circuit suflicient' to stop or substantially reduce the plate V This current to cause operation of relays 4 and'5. occurs as follows:'

On closure of cam switch 8, the-circuit previouslyprepared through relay winding [0 is closed tothe power source indicated as the opposite side of which may be grounded. This closes armatures I0a and-10d against fixed contacts Hlb and I Be and opens the former connection between Illa and tile. Closure of lim against lllb locks relay ID in, as it will be observed that this circuit no longer includes cam switch 8, and the opening of the cam switch will not openrelay H). In the I have shown only two positions, corresponding to motor circuit, and ole-energizing clutch coil M. The motor is stopped, and likewise condenser 1 and cam 8, and the apparatus will remain in this position.

, distance through which the condenser turns after the motor circuit is opened will be substantially constant for any. particular apparatus, and may closed position of the relay 10, it will be observed that the crystal I 2 is connected through armature Md and'fixed contact me tothe workcircuit.

When'the tuning 'ofjthis circuit approaches the resonance frequency as determined by crystal l2, a voltage'will be generated in the work circuit, rectified by rectifier 2, and will serve to reducethe plate current of tube3 to the pointwhere relay 4 be measured and allowed for in such a manner that. the coasting'which intervenes between the opening of the motor circuit and the final position of restis 'justusufiicient to carry the apparatus to the peak of the resonance curve.

' If theoperator desires to switch to the second channel, he will'move the selecting switch l3 from position [3a to position J31). -This firstopens the circuit of relay ;l0, permitting armatures Illa and I lid to moveto back contact'position, thereby disconnecting crystal l2 from the work circuit. Since no voltage is' now being. produced by the-work circuit,-relay,4 willbe'energized, closing relay 5,

energizing clutch coil [4, and starting the motor. A circuit through relay 9 is'now preparedthrough armature 9a, back contact 9c, to the cam switch fixed contact 8b; but this circuit will not be completed untilthe cam switch 8' has completed a cycle. s z 5-. i

While thiscycleis being-completed, condenser 1 .is. likewise rotating through a complete cycle.

When the cycle is completed, cam switch 8 is closed, and ,thewindin'gor relay 9- energized,

' thereby closing armature 911 against front contact 96; and armature-9a ismoved' from back contact Bcto front; contact 9b. This locks inrrelay '9, since the energizingwinding 'is nowuconnected through contacts 911 andfib'dire'ctly-to th'e'source of'power,

and also connects crystal I I to the work circuit.

1 The motor will continueto operate as before until-the voltage producedby the work circuit is sufficient to'reduce theiplate current of the tube 3 toqthe 'pointarw-hererelay 4 opens; thus operating the; motor rcircuit, whereupon rotation of condenser 'l'stops asalready explained, the apparatus nowbeingtuned to the second frequency; channel: I

In" the :.operation offlthe circuit described,

careful adjustment of both relays 9(and ID is necessarybecausaas will be noted, each of these relays disconnects its .own power in switching fromvback contact position 'to front contact position, in. the latter of:which itis locked in. While careful adjustment of thes'e' relays is required, I have found thatit-is-entirely feasible to arrange the. apparatus tooperate as described.

This assures positive opera'tionunder the condition shown by-Fig12rwhere'the three resonance curves shown represent three channels overlapping: closely,gand under which conditions the voltage impressedon the control tube might be 'ment, or-combination which vention or discovery. T a l -Whi1e I have shown and described certain preferred embodiments of my invention, it will be 'iunderstood that smodifications and changes may be made without departing from the spirit andscope of my invention, as will be apparent to, those skilled in'the artw- Iclaim: v vr 1'. In automatic tuning apparatus, in combination, a frequency determining element; "a work c'ircuit including'a power source'for' 'delivering energy limitedto a frequency determined by said element, said work circuit having a variable tuning instrumentality operable through successive tuning cycles, power means for varying said instrumentality, 1 energy v responsive means receiving energy from "said work circuit for interrupting operationof said power means in response to delivery by said work circuit to said energy responsive means of a predetermined level of energy, and meansfor" causing operation of said power means to move said tuning instrumentality through completion of one tuning cycle irrespective of the'levelof energy of said work circuit, said last mentioned means comprising a relay for closing a circuit to eon nect said frequency determining element to said work circuit, a normally open switch inte'rpos'ed in circuit with the energizing winding of said relay, and meansfor closing said switch once only in each tuning cycle. 2 In automatic tuning apparatusin combination, a frequency "determining element; a

I- claim as my inwork circuit including apower source"fdrde-' livering energy limited to a frequency determinedby saidelement', said work circuit having a variable tuning instrumentality operable through successive tuning cycles, power means for varying said instrumentality, energy responsive means receiving energy from said work circuit for interrupting operation of said power means in response to delivery by said work circuit to said energy responsive means of a predetermined level of energy, and means for causing operation of saidpower means to move said tuning instrumentality through completion of one tuning cycle irrespective of the level of energy of said work circuit, said last mentioned means comprising a relay for closing a circuit to connect said frequency determining element to said work circuit, a normally open switch interposed in circuit with the energizing winding of said relay, and means synchronized with said tuning instrumentality for closing said switch once only in each tuning cycle.

3. In automatic tuning apparatus, in combination, a frequency determining element, a work circuit including a power source for delivering energy limited to a, frequency determined by said element, said work circuit having a variable tuning instrumentality operable through successive tuning cycles, power means for varying said instrumentality, energy responsive means receiving energy from said work circuit for interrupting operation of said power means in response to delivery by said work circuit to said energy responsive means of a redetermined level of energy, and means for causing operation of said power means to move said tuning instrumentality through completion of one tuning cycle irrespective of the level of energy of said work circuit, said last mentioned means comprising a relay for closing a circuit to connect said frequency determining element to said work :c'ircuit a) normally open switch interposedin circuit with a the energizing-winding of said relay, means for closing-said 'switchwonce only in each tuning cycle, and a circuit completed by said'r'elayon :closure for energizing saidxrelay independently of said normally open switch 4. In, automatic tuning apparatus,- 1' in combi+ nation, a frequencyldetermining elementganwork circuit including "a' power source fon delivering energy limited to :a frequency determined; by'said element, said work circuit having a variable -:tun-'- ing instrumentality operable through'isuccess'ive tuning: cycles, power means for varying said instrumentality; energy responsive means receiving energy from said workcircuit forinterrupting operation of said powermeans iniresponse to delivery by saidz'work circuit= to said energy "responsive means i of a predetermined level of 1 energy and meansfor causing operationof said power means to move: said-ltuningl instrumentality through completion of one'rtuning cycle irrespective of the level of energy of "said work circuit, said last mentioned means comprising a: relay for closing a circuit to connect said frequencyidetermining element to .said'work circuit,a normally open switch interposed inr circuicwith the: energizing winding of said relay, means synchronized with said tuning instrumentality 'forclosing said switch once only in each tuningcycle, and a circuitcompleted by saidrelay on closure for energiz ing'said relayindependently f said normally open switchl 1 H5. :In automatic-tuning apparatus, in combina tion, vafreq uency determining element-a frequency selecting switch for selecting said frequency determining element, a :work' circuit includinga power source for delivering energy limited to: a frequency determined by said element, said work circuit having a variable tuning instrumentality operable through successive tuning cycles, power means for varying said instrumentality, energy responsive means receiving energy from said work circuit for interrupting operation of said power means in response to deliveryby said work circuit to said energy responsive means of a predetermined level of energy, and means for causing operation of said power means to move said tuning instrumentality through completion of one tuning cycle irrespective of the level of energy of said work circuit, said last mentioned means comprising a. relay for closing a circuit to connect said frequency determining element to said work circuit, a normally open switch interposed in circuit with the energizing winding of said relay, means for closing said switch once only in each tuning cycle, and a circuit completed by said relay on closure for energizing said relay independently of said normally open switch, said circuit including said frequency selecting switch.

6. In automatic tuning apparatus, in combination, a frequency determining element, a ,frequency selecting switch for selecting said frequency determining element, a work circuit including a power source for delivering energy limited to a frequency determined by said element, said work circuit having a variable tuning instrumentality operable through successive tuning cycles, power means for varying said instrumentality, energy responsive means receiving energy from said work circuit for interrupting operation of said power means in response to delivery by said work circuit to said energy responsive means of a predetermined level of energy, and means for causing operation of said power means to move said tuning instrumentality through completion of one tuning cycle irrespective of the level of energy *oi: said workficircuit, a said last; mentioned means-'acomprisingraarelayforclosings: circuit to connect' said'z frequency determining: element to said work circuit,v as normally:open-switchxlnterposed: in: circuit: with; the energizing: winding of v work circuit including-a: power: source :for delivering energy limited to avfrequenc'y determined by the; selected frequency-determining aelementoper able vthrough 'successivituning; cycles,- saidzwork circuithavinga variable tuning instrumentality, power: means for: varying? saidr instrumentality, energy: responsive means'receivingr energyitfrom said Work? circuit for interrupting operation of said .Ipowermeans in resp'onsei to=delivery by'said work circuit; to said" energy responsive means of a predetermined level of: energy; andqmeans" for causingroperation. ofxsaid power means to 'moive said. tuning: instrumentalityr through completion ofw'one' cycle. irrespective of.= the-level of energy: f: said work: circuit, 2 said: last mentioned means comprising a relayf'or each frequency deitermining element for closing a: circuit to connect said frequency determiningwelemente to'. said work circuina normally open switch interposedinicincuitWith-the energizing windingof each of said relays; means. for; closing said: switch onceti'only in reach tuning. cycle; and a circuit-ior' each relay,

completed by "the relay on closure for: energizing said relay independently of saidnormally open switch, each: of said circuits including said' frequency selecting: switch. a i

8. ,In automatic tuning apparatus, 1I1'COmbiIl8;- tion; ar plurality of: frequency: determining elements;:a frequency. selecting switch for selectin one of said frequency; determiningelements, a

work circuit including a. power source fordelivering energy limitedrto a frequency determined by the selected frequency determining element operable-through successive tuningicycles, said work circuit having a variable :tuning instrumentality, power. means for varying said .instrumentality,

energyr responsive means .--receiving energy from termining element-for closing a circuit to connect said frequency determining element to said work circuit, a normally open switchinterposed in circuit with the energizing windingof each of saidrelays, means synchronized withsaid tuning instrumentailty fonclosing said; switch once only in each tuning cycle; :and a circuit for each relay,

' completed by the relay on closure for energizing saidrrelay independently of said normally open switch each of sa d vcircuits including said frequencyselectingswitch 1' v QIAMESFELCI-IAIDIDLER; 

